An example of a transponder arrangement is described which consists of an interrogation device and a responder. The interrogation device includes a transmitter which via an antenna can send to the responder an interrogation signal to which the responder reacts by transmitting a message stored therein. Said message can then be received and evaluated by the interrogation device. The responder has very small spatial dimensions and can therefore be implanted for example in animals so that said animals can then be identified by using the interrogation device in accordance with the responder contained in them. By means of an antenna the transmitter in the interrogation device generates a predetermined field strength which is necessary to reach responders lying within a predetermined distance from the interrogation device by the interrogation pulse. However, the use of field strengths as high as desired for increasing the range is not readily possible because due to official regulations in most countries certain upper limits are stipulated for the admissible field strengths depending upon the particular transmitting frequency selected. These upper limits differ from country to country so that when using the interrogation device in different countries it must be assured that the particular upper limits applicable to the field strength of the radiated HF signal are not exceeded.
Observing the field strength upper limits presents difficulties even within one country if it is intended to operate the interrogation device with different interchangeable antennas. This replacement of the antenna may be desirable for adaptation to different uses. For example, to achieve various directional patterns different antennas can be connected to the interrogation device. Thus, when changing the antenna as well it is always necessary to ensure that the admissible field strength upper limits are not exceeded with any of the antennas made available to the users.
The different upper limits of the admissible field strengths applying in various countries present problems to the manufacturer of interrogation devices when it is intended to offer one and the same interrogation device, i.e. a device having always the same transmitting section, in various countries. Supplying devices with differently set transmitting powers in accordance with the country of use would result in a considerable increase in the production and storage costs.